Kramar



E. KRAMAR RADIO BEACON Feb. 2l, 1956 3 Sheets-Sheet l Filed June '7,1951 INVENTOR Ernst Kram ar ATTORNEY Feb. 21, 1956 I E, KRAMAR 2,736,022RADIO BEACON Filed June 7, 1951 3 Sheets-Sheet 2 INVENTOR. 5,718? KramarFeb 21, 1956 E. KRAMAR l 2,736,022

RADIO BEACON Filed June 7, 1951 3 Sheets-Sheet 3 Fig. 5

IN V EN TOR.

Erna? Kramar I fdirection isdetermined by'the elapsed time betweenynorth identification and the passing of the minimum .through thereceiving equipment, measured at the posi- Ation bymeans of astop watch.However stop Watch lmethods.areirnpractical and have the disadvantagethat .a.cornplete.revolution ofthe beamed radiation has to .important-for ship :navigationl place ,of .thecommon light beacons, or inaddition thereto, .especially .when visibilityis poor.

.to .the .minimum .position .respecttoa Vxeddirection in the revolvingradiation,

United States l2,736,022 .RADIonEACoN vErnst KramarfPforzheimyGermany,assigner to linternational -Standard'Electric Corporation, New York, NY., a corporation of Delaware Application June '7, 1951, Serial No.230,298 Claims priority, application. Germany June 9, 1954) 6 Claims.(Crew- 106) There are known radio beacons with a rotating directionalpattern having a single or multi-leaved beam radiation with outstandingminima. `When these minima pass through a predetermined directiomforinstance north, a particular non-'directive,identification is sent out.The the be completed before a determination of direction is possible.

Such rotating radio beacons are, among other things, V,They can be usedin Ithas .already .been suggested to avoid the stop watch measurement byannouncing the direction corresponding ofthe directional beam with whenarevolving radio beacon with rotating minimum of .a directional,radiation is used. Such beacons, for instance, may Vcomprise adirectional antenna system 1n .conjunction withanon-directional antenna.The directive diagramis modulated withaudio frequency, andthe radiation.ofthe directive diagram interrupted at times, in order that theidentification can be sent over the omni- ,directionalaerial during thepause.

,modulation of .the revolvingbeamed radiation, and that the-direction.corresponding to the minimum position of this directiveradiation is continually announced over thetransmitting system.According to the described example a rotating directive diagram isperiodically Y changed in its position in a fast rhythm in comparison tothe,rotatingA frequency, during rotation, whereby two rotating directivediagrams alternately result, and the direction .corresponding to theequal signal value of both ,diagrams isannounced over .this Vdirectiveradiation system.

In completing the ideaof this invention it is further suggested that therotating radiation system is supplied by the .transmitter modulated.with the identification announce- 'ment andinV addition. thereto,supply a push-pull device with the co-phasal output voltage of thesender which .is controlled anti-phasally by the phase modulation (ofanV audio4 frequent keyfrequency), whereby the output ofthepush-pulldevice supplies a rotating directive aerial system, .i..-e..the radiation of which having a distinct minimum (i. e. v.an 'S-formedAcharacteristic which, in conjunction with'afurther radiation of thesame freatent "O transmitter which operates Yqueucy lgives acardioidshaped diagram). Two tubes which are alternately blocked, can beadvantageously .used as a phase modulation push-pull device, the grids.of which are supplied co-phasally with the high frequency voltage ofthe transmitter modulated with the identication announcement.

it is often desired that a ne sub-division be accomplished in additiontothe coarse Vdivision of the region around the rotating beacon havingat least two sectors.. `When a light beacon is used it is appropriate tomark thesections with the colors greenand red and totiuely divide bymeans of digitswhich correspondvtotheiangle of fixed 'directionfor`instance north. In orderto fix a position during a first revolutionthe section is announced and during a second revolution the exact angleis announced. If it is desired to operate several rotating radio beaconswith the same wave length along a shore strip, then, according to theinvention the individual beacons radiate one Vafter the other changedinacertain rhythm. During a denite period of time only one beaconradiates and rotates as Vdescribed above.

Figure l is a schematic circuit diagram illustrating theradiobeaconshowing one` example of. my invention, and Figures 42 through5 are diagrams illustrating the operating principles of a radio beaconin accordance with this invention.

lThe invention will iirst beV broadly described inconnection WithFigure 1. The character S represents a lwithl any desired wave: length.it is modulated by an identification which has a word, a digit oraletter assigned-to each direction by signals'from source 3 incomparisonto'a referencen direction. 'The output voltage Aof the sender issupplied to an omni-directional aerial 5 on the one hand whichcontinually radiates the identification and on the other handco-phasally to the two push-pull tubes R1 and R2. The twotubes'arefurther anti-phasally controlled by aV phase modulation voltageover thetransformer T1, from 'a switching source 6 the frequency of which' ishigher than therotating frequency of thedirective radiation. Undercertain-conditions it could be practical-not to give this controlvoltage a sine form but to adapt ity more or less'to `a rectangular ortrapezoid form; The condensers C1 and C2 respec- -tively chokes D1andiDz serve to mutually bloclcthe' high frequency and modulationcircuits. Between the center of the transformer T1 andtheconnectedcathodes of the tubesthe grid voltage Gis presentg'between thecenter of the output transformer and the cathodes,the anode voltageY Ais present. The output transformer T2 supplies a directive aerial 1, v2,3, 4, system'in-such a manner, that the direction of current alternatescorresponding to the rhythm of modulation. In the most` simplecase thedirective aerial system may consist of a rotatable frame or simply thetwo radiators' l and 2, which is mechanically driven. By way ofillustration, antennas 1-'5 are shown as mounted on rotatable disc 7.The rotation of the directive aerial system and the proper announcementof the identication must take place synchronously. The motor 9 is showncoupled by shafts l0 and'll torsignal source 8 and disc"7 as indicated.This-shows Van example of mechanical rotation of theantennasfsimultaneously with the-control of' the signal. Theidentification can be recorded on a disk, a film-or steel band which issynchronously drivenwith the directive aerial system.

Operation of the arrangement is as follows: By interaction of thedirective aerial system and the omni-directional aerial a cardioidradiation characteristic results in a manner already known. By means ofrhythmic switching over the'push-pull tubes caused by phase modulationtwo mirrored cardioid diagrams result. The ntersection ,points of bothdiagrams fix the bearing raydeiined by an equal signal value of bothradiations. It rotates with the desired frequency of the rotating radiobeacon. The identification announcement can be clearly heard in thebearing direction. in other directions the key frequency (phasemodulation) is noticeable as an interfering modulation in the head setor loud speaker so that the identification is distorted or completelyundetectable. In order to differentiate between the individual rotatingradiation beacons it is suggested in the invention to announce theidentification name of the radiation beacon for example Bill For thispurpose the phase modulation is interrupted particularly when thebearing ray passes through a predetermined direction such as north,east, south and/ or west.

The disadvantage of this method its ambiguity as two minimum values ofthe interfering modulation occur, spaced 180 degrees. The drawback ofambiguity may be eliminated by the following method.

The method in accordance with the further invention described above isin is characterized by the feature that a directional pattern having butone distinct minimum over a S60-degree range is modulated stepwise by aphase angle less than 90 under its rotation at a rate high with respectto the frequency of rotation and preferably within the audio range, sotwo patternsV are obtained which intersect between the minimum points ofeither diagram, and that the direction corresponding to a minimum ofinterfering modulation at the crossover point of the switched patternsis modulated continuously on the carrier frequency of the directionalradiation as a varying identification.

The pattern-switching causes in the receiver an interfering modulationwhich however disappears at the crossover point of the two diagrams asmuch as with dot-dash or A-N keyed localizers. In this manner the knownmethod where directions are determined by the absence of the directionalradiation or the modulating tone of a rotating cardioid-like pattern isextended into a method where the direction is determined by thedisappearance of an interfering modulation, i. e. an audio frequency aswell, While however unlike the so far known methods a carrier signal isleft in the direction of minimum interfering modulation.

The directional antenna array is further provided with an identificationcorrelated with the respective azimuth position of the interferingmodulation which continuously indicates the sequence of azimuthpositions. The azimuth identification is clearly audible only in theabsence of interfering modulation while in all other azimuth directionsit is disturbed by the interfering modulation.

In Figs. 2 through 5 the method is illustrated in detail. By means of adirectional antenna array which for example comprises four outerradiators at the corners of a square and a center radiator with theirfeed phases so chosen that each of the two sets of diagonally oppositeantennas has its two antennas out-of-phase to each other, while the twosets of antennas are fed in phase quadrature. The phase of the centerradiator is chosen equal to that of one of the outer antennas. Arotating R.F. iield is set up the radiation pattern of which is muchsimilar to a cardioid in that it dips to a sharp minimum. This patterncan be rotated either mechanically by turning the whole antenna array,or electrically by means of goniometer equipment. In accordance with theinvention, the currents feeding the antennas are modulated stepwise intheir relative phases in a way that the radiation pattern set up at agiven set of phase conditions is switched back and forth at a rate highwith respect to the speed of rotation through an angle less than 90, forexample 30. This gives rise alternately to the radiation patterns markedA and B in Fig. 2 which intersect at point S. lf patternswitching iseffected at an audio rate, an audible interfering modulation is causedin the receiver which disappears only at the crossover point and in theregion where the two diagrams cover up. Upon proper choice of theradiation pattern, i. e. in a way that the two alternatiugly keyedpatterns cover each other in the region opposite to the minimum, nofurther crossover will result.

This particular radiation pattern where to al1 practical purposes thecardioid-like pattern is circular in the region opposite to the minimum,can be attained by proper choice of the relative current intensitiesfeeding the individual radiators of the directional array. If, forexample, two opposite outer radiators are fed with unit currentintensity, the center radiator with an intensity of two units, and thetwo remaining opposite radiators with an intensity of V 3 units, thiswill result in an elliptic rotating iield and a radiation pattern whicheverywhere except at its minimum comprises contour lines which arevirtually circles.

The production of an elliptic rotating field is illustrated in Fig. 3.The parts l, 2, 3, 4 and 5 are individual radiators comprised in thedirectional system. The opposite outer antennas Il and 2 are fed atopposite phases with unit intensity, while the opposite outer antennas 3and 4 are also fed out-of-phase, but at an intensity of V3 units and thecenter antenna 5 is fed with an intensity of two units in phasequadrature to three of the outer radiator units. This feed scheme willcause an elliptic rotating field D and a radiation pattern K, thecontour lines of which are virtually circles in the region opposite tothe minimum.

Fig. 4 shows the alternately keyed patterns in rectangular coordinatesunder the assumption that the directional array is fed in the manneroutlined above and that pattern switching, or stepwise feeder phasemodulation through i30 is carried out. Here A represents one, and B thealternate radiation pattern which intersect at point S, and also at thepoints s1, s2, s3. At all of these crossover points the interferingmodulation caused by patternswitching will disappear with curve Cillustrating the amplitude of the interfering modulation signal. As isapparent, the interfering signal increases strongly near the desiredbearing beam S.

As, at the transmitting end the directional pattern is rotating, thepilot of an aircraft will observe first a heavy increase in theinterfering modulation followed by absence of the latter near therotating bearing beam which makes the identifying modulation clearlyaudible. Once the bearing beam has passed, the interfering modulationwill increase again followed by a decrease. At points s1, s2, s3 theinterfering modulation will indeed disappear too, and the identifyingmodulation will be audible also over the range to 230, but this willintroduce little trouble with an omnidirectional range, as the bearingbeam proper is defined by its accompanying strong interfering modulationat either side, and confusion will hardly be possible with therelatively large angular range 70 to 230, the less so as the identifyingmodulation varies steadily throughout this range where it is distinctlyaudible.

As the two patterns A and B are identical, the spurious bearing beamss1, s2, s3 can be entirely eliminated, if pattern-switching in thementioned embodiment is done with L55 This condition is shown in Fig. 5which illustrates that only one crossover point S of the two patterns isleft. It is true that between the angles and 150 the interferingmodulation will disappear as well, butas outlined abovenobody willmistake this range for a bearing beam.

lt should be clearly understood, that this description is made only byway of example and not as a limitation to the scope of my invention asset forth in the objects and in the accompanying claims.

`tit/hat is claimed:

l. An omnidirectional radio beacon comprising means for radiating energyin a directive pattern having a null point, means for effectivelyrotating said pattern at a predetermined speed, means for transmittingsignals indicative of the direction of said null point insynchronization with said effective rotation, and means for alternatelyshifting the phase of energy in said directive pattern at a raterelatively high with respect to said predetermined speed, whereby saidsignals will be obscured by the phase modulation of said phase shift,except in the direction of said null point.

2. A radio beacon comprising means for radiating energy comprising arotatable directive radiator, and an omni-directional radiator, a sourceof radio frequency energy, means for alternately shifting the phase ofsaid radio frequency energy at a rate high with respect to the speed ofrotation of said radiator, means for applying said alternately phaseshifted energy to said directive radiator, a source of directionindicating signals synchronized with said rotation of said directivepattern, means for modulating energy from said source with said signals,and means for applying said modulated radio frequency energy to saidomni-directional radiator.

3. A beacon according to claim 2 wherein said means for shifting thephase of said energy comprises, a pushpull device, means for applyingsaid radio frequency energy to said device in parallel, means forapplying a phase shifting signal to said device in parallel, and meansfor extracting energy from said device in push-pull.

4. A radio beacon according to claim 2 wherein said rotatable directiveradiator comprises four radiators, positioned at the corners of asquare, and said omnidirectional radiator comprises a radiatorpositioned at the center of said square, further comprising means forapplying current to respective pairs of diagonally opposite radiators,and said center radiator, in the ratios of References Cited in the fileof this patent UNITED STATES PATENTS 2,129,094 Greig Q Sept. 6, 19382,212,233 Kolster Apr. 20, 1940 .2279.931 Cocker-ell et al. Apr. 7, 19422,303,0 l9 Morawetz Jan. 12, 1943 2,424,079 Dome July 15, 1947 2,513,493`Kliever July 4, 1950 2,578,961 Aribert Dec. 18, 1951 FOREIGN PATENTS467,9 t3 Great Britain June 9, 1937 114,495 Australia June 24, 194()866,707 France May 31, 1941 960,186 France Oct. 17, 1949

